1. Field of the Invention
This invention relates to an apparatus for combining programmed amounts of materials, and more particularly to a conveyor system in which materials discharged from a metering device are combined and passed through the conveyor.
2. Prior Art
Because the majority of products sold today are a combination of ingredients which are mixed, packaged and sold as a finished product, the process of combining various components to form a complete mixture is used in numerous fields. In this process there is a need, however, for more than the ability to merely combine elements. The system used must be capable of accurately measuring the individual components prior to combining them as well as designed to repeat the combining sequence over a large number of cycles without any cross contamination between each individual combination.
The method of sequentially combining elements to form successive combinations of components has generally been by means of a screw auger conveyor adapted to accept the various components to make up the composition. Generally, a screw auger is housed within a conveyor shell and is rotated to carry the individual elements along the conveyor as they are deposited therein to a collecting point. With the removal of the components from the screw conveyor, additional elements to be combined are again deposited within the conveyor and the process is repeated sequentially for repeated mixing of a predetermined amount of each element.
Use of the screw auger as the conveyor means has presented several problems. A primary problem is the cross "contamination" of materials between successive combining procedures. Because of the clearances required between the extremities of the screw conveyor blade and the conveyor shell, materials being moved through the conveyor are not completely removed from the system prior to subsequent combining steps. Therefore, the material remaining in the conveyor shell from previous runs contaminates successive mixtures. Such contamination causes nonuniformity between the mixtures, and where biologically active materials are combined, the contamination by a small amount of another biologically active material would render the system unusuable.
Furthermore, most screw conveyors require substantial power to operate the auger and such power requirements increase substantially with any increase in the length of the conveyor used. The operation is by brute force of the turning screw auger against the material dispensed within the conveyor system. The friction in the system between the materials being moved through the conveyor and the walls of the conveyor add to power requirements necessary to drive the screw auger. Additionally, there is a tendency of material to jam between the outer extremity of the screw blade and the walls of the conveyor shell thereby increasing the force required to drive the system.
Metering of the components dispensed into the conveyor system is also of critical importance to an accurate combination of components. Most particulate material used as elements in combinations of materials are heterogenous in nature in that they are comprised of both large particles and smaller particles randomly dispersed in the mixture. The metering system used to dispense the components making up the final composition must have the capability of dispensing quantities having essentially the same mixture of coarser particles and more finely divided material so that the same mass of material is present in the two volumes.
To accomplish this result, the metering device must be capable of placing the material in a state of uniform compactness so that successive volumetric units metered from a quantity of material will contain the same mass and must be capable of handling the material prior to volumetric metering in a manner so that the random distribution of coarser and more finely divided material is not disturbed. The prior art metering and dispensing devices have generally employed vibration in order to feed material from a hopper to a dispensing mechanism. A major disadvantage of the use of vibration is that, while rendering masses more able to flow, it also causes the particulate material to stratify. That is, the more finely divided material moves to the lower layers resulting in a concentration of the larger particles in the upper layers.